Cytotoxic effects of zinc oxide nanoparticles on cyanobacterium Spirulina (Arthrospira) platensis

Background The extensive usage of zinc oxide nanoparticles (ZnO NPs) in industrial and consumer products raises the risk of releasing their residues into the aquatic environment. The presence of ZnO NPs in the aquatic environment could potentially cause cytotoxic effects on aquatic organisms. Thus, investigating the cytotoxic effects of ZnO NPs on microalgae, which form the base for the food web of aquatic biota, is essential to gain information regarding the ecotoxicological effects of metallic oxide nanoparticles in the aquatic ecosystem. Therefore, the present study has investigated in detail the assorted cytotoxic effects of ZnO NPs on S. platensis using various concentrations of ZnO NPs (10–200 mg/L) from 6 to 96 h to explore the dose- and time-dependent cytotoxic effects. Methods The cytotoxic effects were all assessed through quantification of loss in cell viability, reduction in biomass and decrease in photosynthetic pigments such as chlorophyll-a, carotenoids and phycocyanin. The surface interactions of nanoparticles and the subsequent morphological alterations on algal cells were examined by optical and scanning electron microscopy (SEM). The intracellular alterations of algal cells were studied using transmission electron microscopy. Furthermore, Fourier transformed infrared (FTIR) spectrum was obtained to investigate the involvement of algal surface biomolecules in surface binding of ZnO NPs on algal cells. Results The treatment of ZnO NPs on S. platensis exhibited a typical concentration- and time-dependent cytotoxicity. Results showed a significant (p